I know my local music store restrings all their basses with D'Addario Nickle Round Wounds. But GC might use different ones. They're almost certainly rounds, though.
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Member of Squier Owners Club, The Under 21 TBer's Club #30
99% that they are 45-105 guage, roundwound. Probably nickel too because they are slightly cheaper...As for the brand it's hard to know and Ibanez doesn't state it on their website. I'd say a good new set will probably be an upgrade from the stock strings, especially if it stayed on the GC floor...
Is Mike Mills using nickel rounds here? You can see near the start how the strings shine and they sounds brighter than flats. http://www.youtube.com/watch?v=oJlvgHwemXE